Spitzer Space Telescope - General Observer Proposal #60094


Faint Stellar Distributions in Extended HI Disks

Principal Investigator: Liese van Zee
           Institution: Indiana University

     Technical Contact: Daniel Dale, University of Wyoming

Co-Investigators: 
Daniel A. Dale, University of Wyoming                                 
Kate L. Barnes, Indiana University                                    
Daniela Calzetti, University of Massachusetts                         
Julianne J. Dalcanton, University of Washington                       
James S. Bullock, University of California Irvine                     
Rupali Chandar, University of Toledo                                  
Joannah L. Hinz, University of Arizona                                

Science Category: nearby galaxies (z<0.05, v_sys<15,000 km/s) 
 Observing Modes: IRAC Post-Cryo Mapping
  Hours Approved: 69.6 

Abstract:
In Lambda-CDM models, galactic disks are built through the accretion of small
satellites and through in situ star formation activity. We propose to obtain
deep observations with IRAC bands 1 and 2 to trace the faint extended stellar
component of nearby gas-rich galaxies in order to investigate models of galactic
disk formation and growth. While little is currently known about the full
spatial extent of the stellar component within a dark matter halo, we have
identified a sample of 5 gas-rich galaxies with extremely large HI disks
(D_HI/D_opt > 5) as being the most likely candidates to harbor extended faint
stellar populations. The proposed deep IR observations will allow us to trace
their stellar distributions to unprecedented levels at wavelengths that are
insensitive to both dust extinction and the galaxy's star formation history.
Because our observations are exploratory in nature, we also propose observations
of a control sample of 4 gas-rich galaxies with normal HI distributions
(D_HI/D_opt ~ 2) in order to investigate the extent and nature of faint stellar
populations in the outer disks of galaxies. Comparison of the observed IR
surface brightness profiles with multiwavelength data (from UV to radio) will
reveal the characteristics of the extended disk and provide insight into disk
growth and evolution of gas-rich galaxies.